The present invention generally relates to printhead structures for use in delivering ink to a substrate, and more particularly to a novel orifice plate designed for attachment to a printhead. The orifice plate includes a number of important structural features which enable high print quality levels to be maintained over the life of the printhead. The printhead and orifice plate are also characterized by improved durability levels.
Substantial developments have been made in the field of electronic printing technology. A wide variety of highly-efficient printing systems currently exist which are capable of dispensing ink in a rapid and accurate manner. Thermal inkjet systems are especially important in this regard. Printing units using thermal inkjet technology basically involve an apparatus which includes at least one ink reservoir chamber in fluid communication with a substrate (preferably made of silicon [Si] and/or other comparable materials) having a plurality of thin-film heating resistors thereon. The substrate and resistors are maintained within a structure that is conventionally characterized as a "printhead". Selective activation of the resistors causes thermal excitation of the ink materials stored inside the reservoir chamber and expulsion thereof from the printhead. Representative thermal inkjet systems are discussed in U.S. Pat. No. 4,500,895 to Buck et al.; U.S. Pat. No. 4,771,295 to Baker et al.; U.S. Pat. No. 5,278,584 to Keefe et al.; and the Hewlett-Packard Journal, Vol. 39, No. 4 (August 1988), all of which are incorporated herein by reference.
In order to effectively deliver ink materials to a selected substrate, thermal inkjet printheads typically include an outer plate member known as a "nozzle plate" or "orifice plate" which includes a plurality of ink ejection orifices (e.g. openings or bores) therethrough. Initially, these orifice plates were manufactured from one or more metallic compositions including but not limited to gold-plated or palladium-plated nickel and similar materials. However, recent developments in thermal inkjet printhead design have also resulted in the production of orifice plates which are produced from a variety of different organic polymers (e.g. plastics) including but not limited to film products consisting of polytetrafluoroethylene (e.g. Teflon.RTM.), polyimide, polymethylmethacrylate, polycarbonate, polyester, polyamide, polyethylene-terephthalate, and mixtures thereof. A representative polymeric (e.g. polyimide-based) composition which is suitable for this purpose is a commercial product sold under the trademark "KAPTON" by E.I. du Pont de Nemours & Company of Wilmington, Del. (USA). Orifice plate structures produced from the non-metallic compositions described above are typically uniform in thickness and highly flexible. Likewise, they provide numerous benefits ranging from reduced production costs to a substantial simplification of the overall printhead structure which translates into improved reliability, economy, and ease of manufacture. The fabrication of polymeric/plastic film-type orifice plates and the corresponding production of the entire printhead structure is typically accomplished using conventional tape automated bonding ("TAB") technology as generally discussed in U.S. Pat. No. 4,944,850 to Dion. Additional information regarding polymeric, non-metallic orifice plates of the type described above is provided in the following U.S. Pat. No. 5,278,584 to Keefe et al. and U.S. Pat. No. 5,305,015 to Schantz et al. (incorporated herein by reference). Also of interest is co-owned U.S. Pat. No. 6,155,675 to Van Nice et al. which is likewise incorporated herein by reference. In this document, a number of approaches are outlined for improving the overall durability of polymeric film-type orifice plates. For example, in one embodiment, a protective coating is applied to the top surface and/or the bottom surface of the orifice plate. Representative coatings include diamond-like carbon (which is also known as "DLC"), at least one layer of metal (e.g. chromium [Cr], nickel [Ni], palladium [Pd], gold [Au], titanium [Ti], tantalum [Ta], aluminum [Al], and mixtures thereof), and/or a selected dielectric material (e.g. silicon nitride [Si.sub.3 N.sub.4 ], silicon dioxide [SiO.sub.2 ], boron nitride [BN], silicon carbide [SiC], and a composition known as "silicon carbon oxide"). This approach is designed to improve the overall abrasion and deformation resistance of the thin-film orifice plate structure and avoids "dimpling" problems associated with these components (namely, the undesired formation of various indented regions on the orifice plate member). Furthermore, the overall durability of the completed structures is particularly enhanced through the use of DLC and the other compositions recited above.
However, other important factors must also be considered in order to produce a printhead using a non-metallic orifice plate which is capable of generating clear, distinct, and vivid printed images over prolonged time periods. For example, a condition known as "ruffling" or "ruffles" can occur in printheads using thin-film polymeric (e.g. plastic) orifice plates of the type discussed herein. This condition can cause a significant deterioration in print quality if not controlled. Thermal inkjet printers of conventional design typically employ at least one wiper element (normally produced from an elastomeric rubber, plastic, or other comparable material) in order to keep the external surface of the orifice plate clean and free from residual ink and other extraneous matter including paper fibers and the like. A representative wiper system used for this purpose is described in U.S. Pat. No. 5,786,830 to Su et al. which is incorporated herein by reference. Printheads which employ thin-film organic polymer-based orifice plates are often adversely affected by the wiping process. Specifically, passage of the wiper element(s) over this type of orifice plate can cause an "uplifting" of the plate structure along the edges of the orifices, thereby creating a "ruffled" appearance with "ridge"-like structures being formed at the peripheral edges of each orifice. This physical deformation of the orifice plate (and the resulting alteration in orifice geometry/planarity) can cause significant changes in ink drop trajectory, namely, the intended pathway to be followed by the ink drop in order to create the final printed image. These undesired changes in orifice plate geometry prevent the ink drop from travelling in its intended direction. Instead, the drop is expelled improperly and is delivered to an undesired location on the print media material (e.g. paper and/or other substrates). Deformation of the orifice plate as outlined above (including the creation of extraneous "ridge" structures around the peripheral edges of the orifices) can also cause the collection or "puddling" of ink in these regions. This situation can further alter ink drop trajectory by causing an undesired interaction between the ink drop being expelled (particularly the terminal portion of each drop or its "tail") with collected ink adjacent the orifices. As a result, print quality degradation occurs over time. These problems are again caused by two primary factors, namely, (1) the thin, flexible nature of the organic polymer orifice plates described herein; and (2) the physical forces imposed on the orifice plates by conventional wiper structures (or other objects which may come in contact with the plates).
In summary, numerous adverse conditions are associated with "ruffling" in a thin-film organic polymer-based orifice plate system ranging from a notable deterioration in print quality to a reduced level of printhead longevity and increased maintenance requirements. Prior to completion of the present invention, a need therefore existed for a polymeric (e.g. plastic) orifice plate system which is highly resistant to the effects of repeated wiping using one or more ink wiper elements and does not experience the ink trajectory problems caused by "ruffling" and "dimpling" as previously discussed. The present invention is designed to accomplish these goals in a highly effective and economical manner. In particular, the novel orifice plate and printhead designs described herein (which will be outlined in considerable depth below in the Detailed Description of Preferred Embodiments section) provide the following important benefits: (1) a substantial increase in printhead/orifice plate longevity; (2) the ability to maintain precise control over ink drop trajectory during the life of the printhead; (3) compatibility of the claimed orifice plate with printing units which employ a variety of different wiper systems that are used to clean the printhead; (4) the avoidance of premature damage to the orifice plate notwithstanding its thin-film polymeric character; (5) the ability to provide a high-durability thin-film polymeric orifice plate structure which can maintain its light and thin profile while preventing the problems discussed above; (6) the capability to (if desired) modify the wettability characteristics of the orifice plate at and around the orifices therein so that proper ink ejection is maintained as outlined further below; and (7) the accomplishment of these goals using one or more techniques which are characterized by minimal cost, complexity, and labor requirements. The present invention therefore represents a considerable advance in the art of printhead design and image generation technology.
Further information regarding the claimed orifice plate and printhead structures (including specific data involving the technical aspects of the invention along with preferred operating parameters and representative construction materials) will be provided in the following Summary of the Invention and Detailed Description of Preferred Embodiments sections. Likewise, the particular manner in which the claimed invention provides all of the above-described benefits will become readily apparent from the detailed information presented in these sections.